Internal combustion engines are operated within a desired temperature range to optimize performance and minimize engine wear/degradation. Running the engine cold (below the desired operating temperature) may result in increased engine wear, tailpipe emissions, and fuel dilution. For example, when too cold, exhaust catalysts will not adequately process the unwanted products of combustion leading to increased tailpipe emissions. Further, heat exchangers such as the cabin heater and other lubricated devices such as the transmission and differential oil coolers may require warmed fluids to function properly. Engines typically run cold during and/or immediately after an engine start because they cool down when not running. Thus, after a long cold soak, the engine system must be heated during and/or immediately after an engine start. Engines also tend to run cold at idle and may require additional warming while running at idle.
One example approach for warming an engine during a cold start is shown by Tuggle et al. in U.S. Pat. No. 4,508,068. Therein, the engine is run rich (the air/fuel ratio is operated rich of stoichiometry) to improve engine starting and warm-up. However, the inventors herein have recognized potential issues with such an approach. As one example, the excess fuel injected while running rich may condense on the cold combustion chamber walls of the engine and wash into the oil pan, thereby diluting the oil with fuel. Fuel dilution reduces the viscosity of the oil and makes it less effective at lubricating engine components leading to increased wear and degradation of the engine components. As another example, not all of the injected fuel may be combusted while running rich because of the increased amount of injected fuel. This incomplete combustion may lead to higher levels of tailpipe emissions while the engine is warming up.
The inventors herein have recognized that by heating the engine with waste heat generated by electrically powered devices in the engine and/or vehicle system, the amount of enrichment during an engine start and/or idle may be reduced. Therefore, the issues described above may be at least partially addressed by a method comprising: powering on an electric motor of an intake boost device to generate heat; absorbing heat from one or more of the boost device and air compressed by the boost device via one or more of circulated coolant and circulated engine oil; and after absorbing the heat, transferring the absorbed heat to the engine by flowing one or more of the circulated coolant and circulated engine oil to the engine. By warming the engine with heat produced by an electrically powered boost device, dilution of engine oil with fuel and tailpipe emissions may be reduced. In particular, the boost device may comprise an electrically driven supercharger and/or an exhaust driven turbocharger that is also at least partially driven by an electric motor (electrically assisted turbocharger). The electric motor of the boost device may generate heat as it runs, and may also heat the intake air that it compresses. Thus, the heat from the hot, compressed intake air, and heat produced by the electric motor itself, may be transferred to the engine via circulated coolant and/or engine oil. In some examples, this heat may additionally or alternatively be used to warm the coolant and/or engine oil.
In another example, an electric motor of the boost device may be powered on, and one or more of coolant and engine oil may be circulated through the running boost device and the engine via one or more of a coolant pump and an engine oil pump, respectively, to warm the engine when a temperature of the engine is less than a desired temperature. Under varying engine operating conditions, different control actions may be performed in addition to powering the electric motor of the boost device and circulating the coolant and/or engine oil. For example, prior to an engine start (when the engine is not running), a compressor bypass valve (CBV) may be opened to allow the boost device to continue to recirculate air in the intake while it is running rather than build pressure in the intake. However, when the engine is running, the CBV may be closed to build intake manifold pressure in anticipation of a vehicle launch (vehicle operator tip-in), and one or more engine operating parameters may be adjusted to limit torque output to a desired torque output level prior to the vehicle launch.
In another example, an engine system may comprise: an oil pump; a coolant pump; an engine block fluidically coupled to one or more of the coolant pump and oil pump, the engine block comprising one or more engine cylinders; an intake boost device at least partially driven by an electric motor and fluidically coupled to the engine and one or more of the coolant pump and oil pump; a boost device bypass valve that enables airflow around the intake boost device in an open position; and a controller. The controller may include computer readable instructions stored in non-transitory memory for: powering the electric motor of the intake boost device to generate heat; powering one or more of the coolant pump and oil pump to circulate one or more of coolant and engine oil through the intake boost device and the engine; opening the boost device bypass valve when the engine is off; and closing the boost device bypass valve when the engine is running.
In this way, an electric motor of a boost device may be used in place of, or in addition to, air/fuel ratio enrichment to warm up an engine. Heating the engine with the boost device may reduce the amount of air/fuel enrichment used to warm up the engine, and/or may eliminate the use of such enrichment entirely, thereby reducing tailpipe emissions. Further, by reducing and/or eliminating the use of such enrichment, fuel dilution of oil may be reduced and/or prevented, thereby better retaining the integrity and effectiveness of the oil in lubricating rotating engine components. By warming the engine oil prior to an engine start, the oil's effectiveness in lubricating rotating engine components may be increased during an engine start, thereby increasing the longevity of the engine. Additionally, the mitigation of such fuel enrichment reduces fuel consumption and increases fuel efficiency.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.